1. Technical Field
The present invention relates to liquid level monitoring systems and more particularly to calibrating and/or monitoring a liquid level in containers or reservoirs.
2. Description of the Related Art
Liquid consumption especially fuel in containers/reservoirs (e.g. fuel tank of vehicles, static fuel tanks of cell phone towers and generators) needs to be monitored to measure efficiency of fuel consumption and control fuel pilferage. Since the containers or reservoirs inherently involve large fuel transactions (e.g., consumption and delivery), it is necessary to monitor an amount of fuel being received and consumed on an ongoing basis. Containers or reservoirs differ in size in vehicles, static fuel tanks of cell phone towers. Thus, human intervention may results in errors and is less reliable over accurate remotely monitoring methods. Manual calibration of liquid level and handling of potentially hazardous and corrosive liquids in such containers is very cumbersome.
Containers of different shape/size will have to be calibrated individually for measuring the liquid level. Typically, fuel level sensors are used for monitoring level of liquid within a tank and are resistive, capacitive, ultrasonic or electromagnetic in nature. Previously attempts have been made to monitor liquid level by measuring and calibrating sensor voltage/current versus liquid capacity by incrementally filling the container or reservoir. However, this process is very cumbersome and time consuming as the reservoir needs to be emptied first, and then filled in an incremental manner while measuring the sensor voltage at each level of filling the liquid. This process is impractical for large tanks in remote areas and may involve risk when the liquid being handled is volatile/inflammable/corrosive in nature.
In another implementation, a pre-calibrated sensor is installed in a liquid tank. This is only suitable for environments where the tank geometry and the sensor type are known upfront and tank geometry along with sensor voltage is constant at every specific level. However, this approach is unsuitable for after market applications as the size and shape of the tanks vary from one to the other. Irrespective of whether the liquid is being consumed or being refilled, at any given moment, it is important to accurately estimate a quantity of liquid in a tank/container. As discussed, a liquid monitoring sensor needs to be installed to accurately calibrate for a signal from the sensor to correspond to an actual amount of liquid which is present at any given time in the tank.
If information regarding the present quantity of liquid in the tank can be obtained from the sensor, a control unit, for example, may be used to indicate a maximum possible distance for an automotive vehicle to travel before the tank has to be refilled or to calculate efficiency of system having a static liquid container. To perform such calculations the accuracy of the information on liquid (e.g., fuel) volume present in the tank/container is critical. As mentioned above, currently tanks are equipped with a liquid level sensor which is adapted for measuring and monitoring the level of liquid surface.
These types of sensors do not take into account the fact that the tank may have a varying cross-section (along any dimension). As a result of a non-uniform and irregular shape and size, it is difficult to obtain an accurate reading of the liquid level. Conventional sensors fail to measure fuel levels when the ignition is turned OFF, since there is no voltage from the battery to the sensor. Accordingly, there remains a need for a calibration system and method that determines liquid level irrespective of the size and shape of the containers/reservoirs, and at all times.